Steering apparatus for automotive vehicle

Abstract: A steering apparatus for an automotive vehicle having a steering mechanism (A) arranged to steer a set of dirigible road wheels (21, 22) in accordance with a steering effort applied to a steering wheel (10), wherein the steering mechanism (A) is designed to preliminarily bias the road wheels (21, 22) leftward or rightward a condition where the steering wheel (10) is placed in a neutral position for straight travel of the vehicle.

Description: The present invention relates to a steering apparatus for automotive vehicles, according to the preamble of the enclosed patent claim 1. Disclosed for example in Japanese Utility Model Laid-open Publication Hei No. 1-144170 or in the EP 0053666 is a steering apparatus of the rack-and-pinion type for an automotive vehicle which includes a tubular housing mounted on the vehicle body to support a rack member displaceably in a lateral direction, a pair of tie rods swingably connected to the opposite ends of the rack member to steer a set of dirigible road wheels in accordance with lateral displacement of the rack member, and a pair of dust boots fixedly coupled at their one ends with the opposite ends of the tubular housing and at their other ends with the tie rods to encompass each joint portion of the tie rods with the rack member. In such a conventional steering apparatus as described above, the steering characteristic is symmetrized in left and right directions to maintain the steering wheel in a neutral position even if the driver causes the vehicle to travel on a flat road without holding the steering wheel. In general, the surface of the flat road is, however, raised at a central portion of the road for drainage. Accordingly, if the driver causes the vehicle to travel on the flat road without holding the steering wheel placed in the neutral position, the steering wheel will be displaced leftward or rightward from the neutral position in accordance with lateral inclination of the road surface. As a result, straight travel of the vehicle may not be maintained. In the case that the road wheels of the vehicle are equipped with radial tires for traveling on a left or right lane of the travel road, a ply-steer residual cornering force caused by the tires themselves acts to restrain the lateral displacement of the vehicle. If the ply-steer residual cornering force is large in excess, the vehicle tends to travel in an opposite direction against the lateral inclination of the road surface. Furthermore, the document WO-A-810 34 72 discloses a steering apparatus having a steering mechanism arranged to steer a set of wheels in accordance with a steering effort applied to a steering wheel, wherein the steering mechanism comprises two helically wound spring elements for preliminarily biasing the road wheels in a predetermined lateral direction in a condition where the steering wheel is placed in a neutral position for straight travel of the vehicle. With such a steering mechanism the straight running characteristic of the vehicle can be enhanced. However, the provision of the spring elements leads to an enlargement of the whole arrangement so that problems can arise when this known steering mechanism is inserted in a vehicle having only a small space for accommodating the mechanism. It is, therefore, a primary object of the present invention to provide a small steering apparatus for an automotive vehicle capable of enhancing a straight running characteristic of the vehicle in a condition where the steering wheel is placed in a neutral position. According to the present invention, the object is accomplished by providing a steering apparatus comprising the features defined in claim 1. For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Fig. 1 is a perspective view of a steering apparatus according to the present invention; Fig. 2 is a partly broken rear view of the steering apparatus shown in Fig. 1; Fig. 3 is a graph showing a characteristic of a left-hand dust boot shown in Fig. 2; and Fig. 4 is a graph showing a characteristic of a right-hand dust boot. In Fig. 1 of the drawings, there is illustrated a steering apparatus of the rack-and-pinion type mounted on an automotive vehicle which is equipped with a right-hand steering wheel 10 to travel on a left-hand lane of the travel road. In the steering apparatus, a steering effort is applied to the steering wheel 10 and transmitted to a set of dirigible road wheels 21, 22 through a steering mechanism A to steer the road wheels. The road wheels 21, 22 each are equipped with a radial tire for traveling on the left-hand lane. The radial tire is designed to cause a ply-steer residual cornering force acting on the vehicle body rightward. As shown in Figs. 1 and 2, the steering mechanism A comprises a tubular housing 31 mounted on a vehicle body structure B and extending laterally in the rearward of each axle of the road wheels 21, 22, a pinion shaft 32 operatively connected to the steering wheel 10 through a steering shaft assembly 11, a rack member 33 supported by the housing 31 to be laterally displaced in accordance with rotation of the pinion shaft 32, a pair of tie rods 36, 37 swingably connected at their one ends to the opposite ends of rack member 33 by means of ball joints J1, J2 and at their other ends to a pair of knuckle arms 34, 35 by means of ball joints J3, J4 to steer the road wheels 21, 22 in accordance with lateral displacement of the rack member 33, and a pair of elastic dust boots 38, 39 fixedly coupled at their one ends with the tie rods 36, 37 and at their other ends with the opposite ends of the tubular housing 31 to encompass each joint portion of the tie rods 36, 37 with the rack member 33. The left-hand dust boot 38 is coupled with the tie rod 36 and tubular housing 31 in a condition where the steering wheel 10 is retained in a neutral position. In this instance, the left-hand dust boot 38 is stretched in a predetermined amount and fixed in place to be applied with a predetermined tensile pre-load F 1 as shown in Fig. 3. Similarly, the right-hand dust boot 39 is coupled with the tie rod 37 and tubular housing 31 in a condition where the steering wheel 10 is retained in the neutral position. In this instance, the right-hand dust boot 39 is compressed in a predetermined amount and fixed in place to be applied with a predetermined compressive pre-load F 2 as shown in Fig. 4. With such an arrangement of the dust boots 38, 39, the rack member 33 is biased rightwards under the pre-load (F 1 + F 2 ) of dust boots 38, 39 in a condition where the steering wheel 10 is retained in the neutral position. In this embodiment, the pre-load (F 1 + F 2 ) of dust boots 38, 39 is determined taking into account of lateral inclination of the road surface and the ply-steer residual cornering force of the radial tires. Assuming that the driver causes the vehicle to travel without holding the steering wheel 10 placed in the neutral position, the rack member 33 is biased rightward under the pre-load (F 1 + F 2 ) of dust boots 38, 39 to steer the road wheels 21, 22 leftward thereby to restrain rightward lateral displacement of the vehicle caused by the ply-steer residual cornering force or side force applied from the radial tires for travel on the left-hand lane. This is effective to enhance the straight running characteristic of the vehicle. In case the ply-steer residual cornering force or side force caused by rotation of the radial tires is small, the vehicle tends to displace leftward due to the lateral inclination of the road surface. In such a case, the mounting condition of the dust boots 38, 39 is reversed so that the pre-load of dust boots 38, 39 acts to bias the rack member 33 leftward. With this arrangement, the leftward lateral displacement of the vehicle is restrained to enhance the straight running characteristic of the vehicle. Although in the above embodiment, the present invention has been adapted to a steering apparatus of an automotive vehicle equipped with a right-hand steering wheel for travel on a left-hand lane of the travel road, the present invention may be adapted to a steering apparatus of an automotive vehicle equipped with a left-hand steering wheel for travel on a right-hand lane of the travel road.

Claims: A steering apparatus for an automotive vehicle comprising a steering mechanism (A) for steering a set of road wheels (21, 22) on a road surface, the steering mechanism (A) including a tubular housing (31) mounted on a body structure of the vehicle to support a rack member (33) displaceable in a lateral direction, and first and second tie rods (36, 37), said first tie rod (36) being connected to one end of the rack member (33), said second tie rod (37) being connected to the opposite end of the rack member (33), a first dust boot (38) being coupled at one end to said first tie rod (36) and at the other end to said tubular housing (31), and a second dust boot (39) being coupled at one end to said second tie rod (37) and at the other end to said tubular housing (31), characterized in that said dust boots (38, 39) are adapted as biasing means biasing the set of road wheels in a predetermined lateral direction when a steering wheel is retained in a neutral position by applying a pre-load force which is predetermined by taking into account a lateral inclination of the road surface and a ply-steer residual cornering force of tires on the road surface. A steering apparatus as claimed in claim 1, wherein said first dust boot (38) is stretched by a first selected amount and fixed in place, said first selected amount corresponding to a first pre-load force (F1); and said second dust boot (39) is compressed by a second selected amount and fixed in place, said second selected amount corresponding to a second pre-load force (F2).

Inventors: OKASITA RYUICHI, SUGIMOTO NAOYASU, OKASITA, RYUICHI, SUGIMOTO, NAOYASU
Applicants: TOYOTA MOTOR CO LTD, TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1994
Main classification: B62D7
IPC codes: B62D7, B62D3